Polycarboxylate polymers, especially acrylic and maleic polymers, are well-known ingredients of detergent compositions and provide various benefits. They are used, for example, as antiredeposition and antiincrustation agents; for detergency building, especially in conjunction with water-insoluble aluminosilicate builders; and for the structuring of detergent powders.
Although various polycarboxylate polymers have been disclosed in the literature as detergent ingredients, only polyacrylates and acrylate/maleate copolymers have found widespread use in commercial detergent products.
Water-soluble polymers of itaconic acid and their preparation are described in U.S. Pat. No. 3,055,873 (Pfizer). These polymers are useful as antiredeposition aids in detergent compositions, and also have the capacity to form clear, extremely tough films.
U.S. Pat. No. 3,405,060 (Carter et al/Monsanto) discloses the use of water-soluble polyitaconic acid and its water-soluble salts as sequestering agents for metal cations.
The use of the water-soluble salts of itaconic acid homopolymers, and of copolymers of itaconic acid with maleic acid, acrylic acid or aconitic acid, as builders in detergent compositions, is disclosed in GB 1 054 755 (Procter & Gamble).
GB 1,530,397 and U.S. Pat. No. 4,124,748 disclose an absorbent crosslinked copolymer of an ethylenically unsaturated carboxylic acid or derivative and a vinyl ester.
EP 506 246A (Rohm & Haas), filed on 9 Mar. 1992 and published on Sep. 30, 1992, discloses the preparation of itaconic acid homopolymers and copolymers which are biodegradable and useful (inter alia) as detergent additives (antiredeposition aids) and scale inhibitors, and for the formation of clear, tough films. Low molecular weights (Mw&lt;10,000, preferably &lt;5,000) are preferred. The only comonomer described is acrylic acid.
EP 193 360A (Procter & Gamble) and U.S. Pat. No. 4,725,655 (BASF) disclose copolymers of a monounsaturated dicarboxylic acid (e.g., maleic or itaconic acid), a monounsaturated monocarboxylic acid (e.g., acrylic or methacrylic acid), and optionally a non-carboxylic monounsaturated monomer, for example, vinyl acetate or acrylonitrile. There is no disclosure of a copolymer containing both itaconic acid and vinyl acetate units. The Procter & Gamble document discloses a terpolymer of acrylic acid, maleic acid and vinyl alcohol (molar proportions 45/45/10).
JP 61 246 294A (Nippon Oils and Fats) discloses a liquid detergent composition with fabric softening properties, containing a polymeric acid or salt derived from acrylic, maleic or itaconic acid. The polymer may optionally contain units of a vinyl monomer, for example, ethylene, butadiene, isoprene, 2-methyl-1-butene, 1-hexene, or isobutylene.
U.S. Pat. No. 4,022,960 (Mima et al/Agency of Industrial Science and Technology) discloses copolymers of itaconic acid salts with vinyl monomers, such as methyl methacrylate, styrene and diallyl diglycol carbamate. The polymers have high refractive index and good transparency, and are useful for the moulding of optical elements such as lenses and prisms.
The literature also contains various disclosures of the polymerization of vinyl acetate with small amounts (up to 9 mole %) of itaconic acid to improve adhesion properties of the polymers. Uses for such polymers include thermal recording media, dispersing agents, and shrinkable fibers, but not detergents. The level of itaconic acid in such polymers is too low for detergency building.
For example, JP 02 163 149A (Kao) discloses a cold-water-soluble film for packaging detergents, drugs etc., the film consisting of a copolymer of 2-8 mole % itaconic acid units, 88-98 mole % vinyl alcohol units and 0-4 mole % vinyl acetate units.
U.S. 3,268,491 discloses low molecular weight of about 700 to 6,000, of .alpha..beta. unsaturated dicarboxylic acids with vinyl acetate, prepared by aqueous-phase copolymerization said to be useful as dispersants or surfactants.
The present invention is based on the discovery that block copolymers of itaconic acid and vinyl acetate may readily be prepared by aqueous solution radical polymerization. As such, or in hydrolyzed form, they exhibit excellent calcium binding capacity, better than that of the acrylic/maleic copolymers currently used in detergent compositions, and surprisingly under some conditions better than that of polyitaconic acid itself. Detergency evaluations have also indicated a kinetic advantage for these copolymers, so that their use is especially beneficial under energy-saving conditions (low wash temperature, short wash time). Film-forming is also better than that of polyitaconic acid. In addition, in automatic dishwashers they provide an anti-scaling and rinse aid composition.
It is also believed, and initial studies have confirmed this, that the presence of vinyl alcohol monomer blocks should facilitate biodegradation.